Many wireless telecommunication subscribers desire to use their wireless terminals in conjunction with telecommunications systems other than their home systems. Subscribers also desire to obtain access to telecommunications services using their existing subscriptions, which access may be independent of their normal telecommunications terminals, through telecommunications systems other than their home systems. Frequently, the need for this occurs while the subscriber is travelling or otherwise outside the service area of their home system. Accordingly, telecommunications systems manufacturers and system operators have developed facilities to permit subscribers to receive services using their telecommunications terminals and subscriptions via a system which may not be the subscriber's home system, provided that the terminal and the serving system are compatible. This feature is often referred to as “roaming”.
Serving roaming subscribers is challenging even when the serving system and home system employ identical technologies. However, where the serving system is implemented using air interface and/or call model technology families that differ from those used in the home system, special challenges arise in providing interworking between such systems due to fundamental differences in message protocols, call models, and the basic structure and facilities of the underlying systems. Moreover, these differences are exacerbated over time as new technologies are introduced into networks containing a range of legacy technologies, and the old and new technologies are required to interwork.
FIG. 1 depicts a known arrangement 100 for the interconnection of selected components of two wireless systems: a “serving” system 110 using one of the conventional North American wireless technologies (such as Analog Cellular (AMPS), TDMA, CDMA, etc.); and a “home” GSM system 112. The term “domestic wireless” (DW) is intended to refer to any of the wireless air interface and call model standards used in North America, including but not limited to those mentioned above. The components shown are selected to illustrate those needed for certain interworking between the systems in order to provide, within the service area of the “serving” domestic-wireless-type system 110, service to a DW mobile station (MS) 114 having a home subscription on the GSM system 112. It will be appreciated that both the serving DW system 110 and the home GSM system 112 have voice capabilities. Typically, the mobile station 114 would be a dual mode terminal which is compatible with one or more of the DW standards (other than GSM) and which is also compatible the GSM standard. The mobile station 114 would communicate with a DW MSC/VLR via a radio link 118, radio base station equipment (not shown), and links connecting the base station equipment to the MSC/VLR 116. The broken line 120 denotes the boundary between the two systems 110 and 112. In order to provide interworking between the systems, the DW system 110 must communicate with the GSM system 112. As is known in the art, the GSM system 112 may provide an Interworking and Interoperability Function (IIF) 122 comprising an HLR emulation function 124 compatible with the DW system 110, connected to a GSM MSC/VLR emulation function 126. The term “function” as applied to these elements is intended to be equivalent to “functional component.” The IIF 122 is connected to the DW MSC/VLR 116 via suitable signaling links, which may optionally include a Signal Transfer Point (STP) 128.
The HLR emulation function 124 of IIF 122 appears to the DW MSC/VLR 116 as any other DW HLR, in that it appears to provide the functions of such an HLR more or less transparently to the DW MSC/VLR 116. The GSM MSC/VLR component of 126 the IIF 122 similarly appears within the GSM network 112 as any other GSM MSC/VLR. The GSM MSC/VLR 126 is connected to a GSM HLR 130. Thus, the IIF 122 provides signaling protocol, call model, and other necessary translations to permit the DW MSC/VLR 116 to perform normal registration, call processing and other transactions with the IIF 122. To the extent the IIF 122 needs information or other resources from the GSM network 112 in order to perform the functions of a DW HLR, the GSM MSC/VLR component 126 may maintain those resources directly or may request them from other elements, such as the GSM HLR 130.
As is known in the art, the MS 114 may register (message 132) with the DW MSC/VLR 116, and the DW MSC/VLR 116 will propagate a suitable Register Notification message 134 (or messages 134a and 134b if a STP 128 is used) to the IIF 122, which will perform any necessary translations, and further propagate resulting GSM protocol registration messages 136 to the GSM HLR 130. Any acknowledgements (not shown) may be similarly be passed and translated in the opposite directions.
FIG. 2 depicts an arrangement 200 similar to that of FIG. 1, except that the serving system 210 and home-system 212 are reversed. That is, in FIG. 2, the serving system 210 is a GSM system and the home system is a DW 212 system. It will be appreciated that both the serving GSM system 210 and the home DW system 212 have voice capabilities. The MS 214, which may be a dual-mode or multiple-mode mobile, or may be a GSM-only mobile containing a Subscriber Identity Module (SIM) corresponding to the subscriber's home DW subscription, may register (message 232) using normal GSM protocols. The GSM MSC/VLR 216 transmits, e.g., a Location Update message 234 to the Interworking and Interoperability Function (IIF) 222.
The IIF 222 of FIG. 2 contains a GSM HLR (or suitable emulator) 224, and a DW MSC/VLR (or suitable emulator) 226. The DW MSC/VLR 226 translates the message as necessary to employ DW protocols (e.g., it may prepare a suitable Register Notification message 236), and transmits it to the DW HLR 230. In this case, because the GSM authentication function is complex and not supported by the DW HLR 230, the GSM HLR 224 must also perform the authentication function. However, the DW HLR 230 may perform the other customary functions associated with registration of the mobile station. Any acknowledgements 238 produced by the DW HLR 230 may be transmitted and translated in the opposite direction.
As is known in the art, a call to the MS 214 while roaming in the GSM system 210 would be initially delivered to the home DW MSC/VLR (not shown), which would consult the DW HLR 230 to determine the location of the MS 210 and provide routing information needed to extend the call to the GSM MSC/VLR 216 for ultimate delivery. In this case, the DW HLR 230 will query the DW MSC/VLR emulating component 226 of the IIF 222 for a Temporary Local Directory Number (TLDN) and the IIF 222 will query the GSM MSC/VLR 216 for a Mobile Subscriber Roaming Number (MSRN). The IIF 222 will send the received MSRN as the TLDN back to the home DW MSC/VLR for it to extend the call to the GSM MSC/VLR 234.
These processes assume that the mobile station 214 and GSM 210 network both have voice/circuit capabilities (although they may also have packet GPRS capabilities). In that case, the GSM HLR 224, the GSM MSC/VLR 216, and the DW HLR 230 are capable of providing traditional mobility management and other functions needed to provide telecommunications services to the mobile station 210, including termination of calls.
However, there may be situations in which a subscriber would be unable to obtain utilize voice/circuit services from a GSM system 210, but would desire to use GPRS services if they were available and roaming were possible. For example, a subscriber may be present in an area in which GPRS (i.e., packet data) service is available, but GSM service (i.e., circuit voice and data) is not available. Similarly, while travelling, there may be available to the subscriber a mobile station or terminal compatible with a GPRS system but not with a GSM system. For example, the mobile station may be a wireless Personal Digital Assistant lacking any voice capabilities.
Unfortunately, existing DW HLRs, such as DW HLR 230 of FIG. 2, are arranged to support circuit-switched voice or data devices only. Such DW HLRs are not equipped to accommodate registrations of terminals in GPRS- or packet-only mode or of terminals that have only GPRS or packet capabilities. Thus, existing DW HLRs are unaware of GPRS- or packet-only registrations. As a result, existing DW HLRs are unable to perform certain services in connection with GPRS- or packet-only mobile stations.
One service the existing DW HLR cannot perform is identification of a Serving GPRS Support Node (SGSN) in order to allow termination of an incoming Short Message Service message to the mobile station. Typically, such messages are initially directed to a Message Center element of the DW network, which element is connected to the DW HLR 230. In DW networks, mobile stations do not attempt packet-only registrations, but rather these mobile stations register in a manner compatible with the DW HLR 230. When a roaming GPRS- or packet-only terminal of a DW-native network registers in the GSM network 210, the DW HLR 230 in the home network 212 has no facility for accepting information about such registration, and in particular, has no facility for storing the identity of the serving GPRS SGSN. Accordingly, when an SMS message arrives at the Message Center of the DW network 212, the DW HLR 230 is unable to provide routing information to enable the SMS message to be forwarded to the serving SGSN for delivery to the mobile station.